It is frequently desirable to be able to provide a downward angle of view from the window of one or both of the entrance doors of a vehicle such as, for example, those of an airplane. This may be desirable for the purpose of observing the outside conditions of the ground close to the airplane without having to open the doors.
To that end, it has been proposed to enlarge the double panes of the window. However, it has been found that the critical downward angle of view is not thereby appreciably improved.
The patent to Norris, U.S. Pat. No. 2,709,136, discloses a prismatic window structure. This is intended for the window adjacent to an airplane passenger. Only a single window is provided and the prism is oriented in a horizontal direction to afford the passenger a better forward view. Therefore, the line of sight is essentially parallel to the fuselage. Thus, the proposed structure consists of a single window and the prism affords only a horizontal view for the passenger. The actual prism extends outside of the airplane and hence increases the wind resistance.
Various prisms have been proposed in connection with an automobile. An example is the patent to Patten et al., U.S. Pat. No. 1,678,479. The prism is disposed near the corner of the automobile windshield to overcome the blind spot created by the corner. To this end, prism strips may be put on the windshield. According to the patent to Buttron, U.S. Pat. No. 1,683,951, an adjustable prism was disposed horizontally near the windshield for observing traffic lights in the car. Similarly, the patent to Johnson, U.S. Pat. No. 1,883,296, discloses a prism which may be tilted in order to better observe traffic lights.
In lieu of a prism, the patent to Heimer, U.S. Pat. No. 3,038,756, suggests the use of two windows in the car, forming an angle with each other.